The present invention provides a high-purity copper sputtering target with minimal deformation during sputtering and high utilization efficiency, and in particular relates to a high-purity copper sputtering target which is useful for forming a copper alloy wiring for semiconductors.
Conventionally, while an Al alloy (specific resistance of roughly 3.0 μΩ·cm) has been used as the wiring material of a semiconductor device, pursuant to the miniaturization of wirings, a copper wiring with lower resistance (specific resistance of roughly 2.0 μΩ·cm) has been put into practical application. As the process for forming a copper wiring, generally adopted is the method of forming a diffusion barrier layer made of Ta or TaN on a wiring or a wiring groove, and thereafter subjecting copper to sputter deposition. High-purity copper of 5N to 6N is normally produced by performing wet or dry purification to electrolytic copper having a purity level of 4N (excluding gas components) as the crude metal, and this is being used as a sputtering target.
As described above, a Cu wiring is now being used pursuant to the higher performance of devices, and the usage ratio thereof is anticipated to continue increasing in the future. Meanwhile, in order to reduce costs, there are great demands for improving the utilization efficiency, and an integrated target is optimal for meeting such demands. Nevertheless, the input power of sputtering is extremely high in recent years, and the problem of deformation is being pointed out.
With a target having a wafer diameter of 300 mm, since the input power is high, a high-strength copper alloy is being used as a backing plate (cooling plate; hereinafter referred to as “BP”) for preventing the deformation of the target during its use. Thus, while the amount of deformation can be suppressed, due to the existence of the BP, the target needs to be formed thinner by that much, and the utilization efficiency of the target will thereby deteriorate.
Moreover, based on a concept that is similar to the integrated target proposed in the present invention, there is also a method of increasing the strength by introducing strain based on ECAE (Equal Channel Angular Extrusion). Nevertheless, with this method, there is a problem in that the main orientation of the sputtering part of the target will also be the (220) orientation that has strain, and this affects the film thickness uniformity.
Upon reviewing the conventional technologies, Patent Document 1 below proposes an integrated target (monolithic target) configured from tantalum, niobium, cobalt, titanium and valve metal, and comprises a flange with an enlarged diameter which is bolted to a coolant (BP). Patent Document 1 further describes giving proof stress and rigidity to the flange part by way of cold working and other processes. While the purpose thereof is unclear, it is assumed that the strength is increased in order to bolt the flange part to the BR Nevertheless, the purpose and details of such increased strength are unclear.
Patent Document 2 below describes integrating a target and a backing plate with a soft metal material made of Al or Al alloy in light of the fact that the mechanical strength of a target made from Al, Al—Ti, or Al—Cr is weak, and proposes suppressing, based on the water pressure of the cooling water, the occurrence of water leakage and abnormal discharge caused by the warpage of the overall target.
In the foregoing case, since Patent Document 2 is based on the premise of the integration of the target and the backing plate, inferiority in terms of conventional utilization efficiency is inevitable.
Patent Document 3 below describes integrating a target and a backing plate with a soft metal material made of Al alloy and further performing cold plastic working thereto in order to cause the micro Vickers hardness to be 36 or higher in light of the fact that the mechanical strength of a target made from Al—Ti, or Al—Cr is weak. In addition, Patent Document 3 proposes suppressing, based on the water pressure of the cooling water, the occurrence of water leakage and abnormal discharge caused by the warpage of the overall target.
In the foregoing case, since Patent Document 3 is based on the premise of the integration of the target and the backing plate, inferiority in terms of conventional utilization efficiency is inevitable. As another reference example (refer to Patent Document 4), there is a sputtering target containing copper in an amount of at least 99.99% by weight, having an average grain size of at least 1 to 50 micrometers, and having a yield strength of approximately 15 ksi or more.
Generally speaking, upon producing a high-purity copper sputtering target, a melted and cast copper ingot is processed into a target shape of a predetermined dimension, and the surface thereof is machined to produce the sputtering target.
In the foregoing case, deformation of the target material needs to be suppressed. When the deformation of the target is minimal, the smoothness of the surface can be maintained, and a thin film with superior uniformity can be formed. Nevertheless, there is no conventional technology that has developed a high-purity copper sputtering target material with the intent of suppressing the deformation of the target without using a backing plate, and improving the utilization efficiency of the target.    Patent Document 1: JP 2005-533930 A    Patent Document 2: JP 2001-107227 A    Patent Document 3: JP 2002-121662 A    Patent Document 4: JP 2005-533187 A